The present invention relates to carburetor control systems for internal combustion engines and in particular to such control systems for small internal combustion engines such as those used with lawnmowers and the like. It is desirable that the speed of internal combustion engines is controlled so that the speed of the engine remains relatively constant under different loading conditions. For instance, in the use of a lawnmower which is powered by an internal combustion engine it is desirable that the selected speed of the engine remain relatively constant despite various loading conditions. Thus, as the lawnmower encounters tall grass which loads the engine down or relatively short grass under which condition the engine has to do little work, the lawnmower speed which has been selected by the operator should remain constant.
In the conventional designs of combustion engines speed controls have been provided which control the carburetor to provide constant engine speed for different loading conditions. Such carburetors are normally provided with a choke valve and throttle valve and have a governor interconnected with the speed control lever and the throttle and choke valves for maintaining constant speeds. The governor conventionally consists of a device which is sensitive to engine speed and has an output shaft or lever which is interconnected with the speed control lever and the throttle valve to maintain constant engine speed.
The speed control lever commonly consists of two parts of which one part is connected by means of a control cable to a manually operable control lever and the other part of which is connected to the governor lever. The two parts cooperate to PG,3 control the choke and throttle valves and are generally interconnected with an adjustment screw by which the high speed of the engine is adjusted. The control lever has an idle position, a start/run position and a choke position. The control lever is connected to the choke valve so that in the choke position the air flow to the engine is reduced and a rich fuel mixture is admitted to the engine.
By means of such type of controls the speed of the engine will remain relatively constant for any of the settings of the control lever because of the interaction of the governor with the throttle valve and the control lever.
Optimum operation of the devices powered by such internal combustion engines requires that the speed of the engine is adjusted to be optimum for the high speed setting of the control lever. A problem with the prior art control systems has been that, when the control lever is moved from the high speed position into the choke position, the interconnection of the control lever with the governor cause the engine to run at a higher speed in the choke setting. This is undesirable since at such higher speed the engine will not operate at its optimum performance level. In addition, the movement of the control lever from the high speed setting to the choke setting may be inadvertent because of improper setting of the control lever by the operator. Thus, engine performance will deteriorate and the implement powered by the engine will not operate at its optimum performance level.
Another problem with the prior art control systems has been that the range of control of the engine speed has been rather limited. Thus, engine speed is generally not controlled at the idle setting of the control lever. This is undesirable since it is possible that the operator will inadvertently load the engine while it is idling and thereby kill the engine so that it must be restarted.